Search results for "Multiple"
showing 10 items of 2678 documents
THE LIMITING EFFICIENCY OF FOUR-BAND CELLS REVISITED
2014
The limiting theoretical efficiency of four-band solar cells is revisited. In previous work, researchers have looked at the theoretical efficiency of four band cells where the smallest of the three sub-band gaps is closest to the valence band and the largest closest to the conduction band. In this work, limits are calculated also for other possible band configurations. In multi-band cells, photon selectivity can be assured by adjusting the band widths. The present work shows that previous authors have put too rigid constraints on the band structure to achieve spectral selectivity. Relieving these constraints gives a considerably higher limiting efficiency for cells with band width restricti…
Kerr frequency comb generation in the normal dispersion regime of dispersion oscillating telecom fiber
2013
The generation of optical frequency combs has a variety of applications from optical metrology to spectroscopy and wavelength division multiplexing. Nonlinear methods to generate frequency combs are based on multiple four-wave mixing (FWM) in highly nonlinear waveguides [1]. The mechanism for the generation of a wideband comb from a CW pump is Kerr-induced phase-matching of the FWM interaction or modulation instability (MI), which requires operating in the anomalous dispersion regime. Such restriction can be circumvented with a cavity geometry, where MI [2] and comb generation [3] may also be observed in the normal dispersion region. Alternatively, one may obtain MI and unequally spaced Ker…
Resolution and field of view improvement in digital holography using a VCSEL source array
2011
We describe a new implementation capable to produce superresolution (SR) and object field of view (FOV) improvement in digital lensless Fourier holography. The method provides synthetic aperture (SA) generation using angular multiplexing incoming from a Vertical Cavity Surface Emitting Laser (VCSEL) source array. SR imaging in a single exposure is obtained after proper digital processing of a multiplexed hologram coming from the incoherent addition of multiple sub-holograms, each one corresponding with a different source of the VCSEL array. FOV improvement in addition with SR imaging is achieved by recording a set of individual holograms obtained by sequential activation of the VCSEL source…
Wavelength-flattened directional couplers for mirror-symmetric interferometers
2005
In the context of guided optics, we derive, analytically and geometrically, a rigorous general criterion to design wavelength insensitive interferometers with mirror symmetry, which are needed for wavelength multiplexing/demultiplexing. The criterion is applied to a practical case, resulting in an interferometer that works on a band wider than 70 nm.
Invariant pattern recognition by use of wavelength multiplexing.
1997
Rotation-invariant pattern recognition can be achieved with circular-harmonic decomposition. A common problem with such a filter is that, because it is only a single term out of the circular decomposition, it does not contain much of the reference object's energy. Thus, the obtained correlation selectivity is low. This problem is solved by use of wavelength multiplexing. First, different harmonic terms are encoded by different wavelengths, and then they all are added incoherently in the output correlation plane. This process leads to rotation-invariant pattern recognition with a higher discrimination ability.
Stimulated Emission in InGaN/GaN Multiple Quantum Wells with Different Indium Content
2005
1. IntroductionLight-emitting and laser diodes for the green to near-UV region are basedon quantum structures with the InGaN active region [1]. The indium contentin the wells is a technological parameter that provides a straightforward accessfor the change in the color of the light-emitting device. However, the redshift ofthe emission peak with increase in indium content is caused not only by a simplealloying, but also by carrier localization due to difierence in In and Ga atomic
Tunable arrayed waveguide grating driven by surface acoustic waves
2016
We present a design approach for compact reconfigurable phased-array wavelength-division multiplexing (WDM) devices with N access waveguides (WGs) based on multimode interference (MMI) couplers. The proposed devices comprise two MMI couplers which are employed as power splitters and combiners, respectively, linked by an array of N single-mode WGs. First, passive devices are explored. Taking advantage of the transfer phases between the access ports of the MMI couplers, we derive very simple phase relations between the arms that provide wavelength dispersion at the output plane of the devices. When the effective refractive index of the WGs is modulated with the proper relative optical phase d…
Resolution improvement by single-exposure superresolved interferometric microscopy with a monochrome sensor
2011
Single-exposure superresolved interferometric microscopy (SESRIM) by RGB multiplexing has recently been proposed as a way to achieve one-dimensional superresolved imaging in digital holographic microscopy by a single-color CCD snapshot [Opt. Lett. 36, 885 (2011)]. Here we provide the mathematical basis for the operating principle of SESRIM, while we also present a different experimental configuration where the color CCD camera is replaced by a monochrome (B&W) CCD camera. To maintain the single-exposure working principle, the object field of view (FOV) is restricted and the holographic recording is based on image-plane wavelength-dispersion spatial multiplexing to separately record the thre…
Design scheme for Mach–Zehnder interferometric coarse wavelength division multiplexing splitters and combiners
2006
I propose an analytical approach to design flattened wavelength splitters with cascaded Mach–Zehnder inter- ferometers when wavelength dependence of the directional couplers cannot be neglected. I start from a geo- metrical representation of the action of a doubly point-symmetrical filter, assuming no wavelength dependence of the couplers. Next I derive the analytical formulas behind its working principle and extend them to the wavelength-dependent case. I also show how the geometrical representation allows one to broaden the class of working structures. © 2006 Optical Society of America
Target localization in the three-dimensional space by wavelength multiplexing.
2002
A method to localize a target in the three-dimensional space is presented. Each different position of the target on the depth axis produces, when captured with a CCD camera, an image of a different size on its sensor plane. The size of this image depends only on the distance between the target and the camera. The use of a white light optical correlator that gives us a different response depending on the scale of the input image permits us to know the depth position of the particular target. The obtained results demonstrate the utility of the newly proposed method.